The present invention relates to a method of manufacturing reinforcing fibers for mineral materials. It also relates to a structural element composed of a fiber-reinforced mineral structural material.
It is known to manufacture pipes, plates and shapes parts such as roof ridges and angled strips, of a mineral structural material with asbestos fibers admixed to the mineral material to reinforce the latter. It has been known for a long time that the asbestos fibers are health hazardous and their utilization necessarily requires the provision of safety measures. Despite this no reinforcing fibers for mineral structural materials as initial materials for structural elements could be found with the physical characteristics as advantageous as the asbestos fibers have, and at the same time which could be not healthy hazardous and thereby would be less expensive.
Some experiments were conducted with metallic fibers. The metallic fibers are, however, too coarse and rigid to be worked without difficulty, and they have a strong tendency to make deposits in water suspensions. Experiments with glass fibers have shown that they have low dispersing characteristics in a water suspension and readily form stoppers which deposit and drain off too fast to make possible machine working. The glass fibers are also expensive. Furthermore, synthetic polyester or acetate base fibers and the like have also been tested with respect to their use for replacing asbestos. These fibers are, however, difficult to disperse, they often form strands in mixing devices, and are not sufficiently hydrophilous. Experiments with wood fibers have shown that they require additional chemical treatment and are difficult to work, since wood lignine and sugar undesirably affect the product strength. Attempts to utilize untreated, that is raw natural fibers, have not been performed, because of the danger of fire, their susceptibility to rot, and the high water absorption.
In addition to the above-mentioned disadvantages of the asbestos, it also has a tendency to form bundles and clusters, because of its structure. This makes difficult the formation of a homogeneous mixture of the asbestos concrete. Approximately 15% of the asbestos component is found to be bundled so as to form so-called nests in the mixture. Because of this it is not, for example, excluded that under the action of weather the nests in the concrete are released and the asbestos is carried away be wind.
Finally, the price of the asbestos should also not be underestimated during all considerations about the efficiency of the asbestos. Asbestos must be imported, which is connected with increase of production costs.